Companies need to design engineering software to obtain emission limits before construction and commissioning the plants to control air pollutants. During the design of plants, all emissions should be studied and measured. Since some emissions are lighter or higher than air, there are different methods for their modeling. These models are used for reviewing the effect of gases on the environment and the best model is the one that can design an accident before dispersion. In this research three software packages, namely PHAST, CIRRUS and SHELL FRED, were compared with a newly-created software for measuring the ground level concentration of H2S and SO2. The software packages were based on the Gaussian model for point sources. In these models, for simplicity, some assumptions were made based on one point source above the ground. According to the results, the new software was similar to CIRRUS in D stability of the air that can be used instead.